I would suspect that the 6GB Quadro will remain a 6GB Quadro and will not filter down to consumer level, however (and this is a big however). Do you know that the FX5800 Ultra 4GB is infact known to consumers as the ASUS M.A.R.S 4GB GTX 295 So who knows maybe some board partner might make a consumer incarnation of the 6GB behemoth which is coming in Q3 2010 in Quadro form.
Now, from what I have read, RAM is useful not only for texture memory and all the fancy video effects and post processing effects, but also GPGPU wizardry too. Apparently stuff like OpenCL, CUDA, DirectCompute Physx etc all love the extra RAM and GPU processing power. So perhaps 3GB cards at the high end are not a "bad" thing.
Who would complain playing a DirectX11 title with high resolution textures (2GB's worth) and then a shedload of computational work which also uses up some of that VRAM for fast execution. (say a further 256MB's worth). Extra VRAM is good when you have it, and certainly a whole world better than hitching, pausing and stuttering if you do not have the VRAM.
Personally I cannot see nVidia releasing an incarnation of the Fermi with LESS than 1GB of VRAM (with the GTX 360 or greater nomenclature), if yeilds are bad and nVidia get bin happy and make the Fermi GPU go down throughout the range to the lowly numbers of GTS 350, 340 then we could see some 768MB models appearing.
IMHO 1.5GB is going to be the base model VRAM with the high end models having 3GB.
This isn't confirmed yet specifications for Quadro and Teslar almost make it safe to assume this will be the desired memory configuration for Fermi.
And yes, I think it is fair to say that we all want the expensive electricity bil, large carbon footprint FPS pushing Monster Fermi
John